Ben Stokes: England wait on scan before Champions Trophy
England all-rounder Ben Stokes is to have a scan to find out the extent of a left knee injury.
Stokes hit a century in the second one-day international win against South Africa on Saturday, but the injury that troubled him in the first ODI meant he could only bowl three overs.
"It comes and goes. I have bad days and good days," he told BBC Sport.
"I'm not sure if it is a worry or not, it might just be wear and tear. Hopefully we'll get a clearer picture."
Stokes showed signs of the problem when bowling at Headingley on Wednesday but after being passed fit to play in Southampton showed no effects during a 79-ball 101.
However, he showed discomfort when bowling as England sealed the series with a thrilling two-run victory.
"It's just the bowling," added the Durham man. "When I land on the floor I get a pain on the outside of my knee, so we just need to find out what that is.
"I was able to bowl today, but at the end of my third over I started to feel it. It's a confidence thing as well. If I feel the knee I don't feel I'm running through the crease properly."
The problem is a concern for England ahead of the Champion Trophy, which they open on Thursday against Bangladesh at The Oval.
"I won't be wrapped cotton wool, it's just part of the game," said 25-year-old Stokes, who is still hoping to play in the third and final ODI against South Africa on Monday.
"We're managing it really well. The physio, doctor and I are doing all we can. Hopefully it will go away."
England captain Eoin Morgan said that Stokes will not be risked on Monday, but he could play as a batsman alone.
"I'm not worried," said Morgan. "We're managing it as we go along.
"He played as a batter for us about a year ago when the same injury crept up. We did a very similar thing against Pakistan where he only bowled three or four overs. We built on it from there and then the injury went away.
"We're monitoring how it react after bowling, because it's bowling that aggravates it. He's crucial to our campaign, so hopefully we'll have a fit Ben Stokes for the Champions Trophy.
"He hates missing out, he always wants to be involved. With the form he's in, I won't be the one telling him he's not playing."
However, former England off-spinner Graeme Swann said the hosts would be "crazy" to take a risk on Stokes.
"He should not play on Monday, even as a batsman. Don't play him, let him get fit so he can bowl. In an ideal world, he'll be fit and bowl 10 overs," he said.
"I don't want to see him playing if it puts as much as a 5% chance of him not being fit as an all-rounder for he Champions Trophy."